Negative electrode material for secondary batteries and method for producing the same

Abstract

Disclosed is a negative electrode material for secondary batteries that can improve the initial discharge capacity, initial efficiency, and life characteristics of secondary batteries, and a method for producing the same. According to the present invention, there is provided a negative electrode material for a secondary battery, comprising an active material having a carbon-coated surface, a conductive material, and a binder, the active material comprising a magnesium-doped composite, the magnesium-doped composite being made of silicon oxide (SiO x , 0.5

Description

Technical Field

[0001] The present invention relates to a negative electrode material for a secondary battery and a method for manufacturing the same, which can improve the initial discharge capacity (IDC), initial efficiency (ICE), and life characteristics of the secondary battery.

Background Art

[0002] The improvement of the performance of secondary batteries is based on the components of the positive electrode material, negative electrode material, and electrolyte.

[0003] Among them, graphite, which is mainly used as a negative electrode material, has a theoretical capacity limited to 370 mAh / g. Therefore, the development of non-carbon-based negative electrode materials such as silicon, tin, germanium, and zinc as materials to replace graphite negative electrode materials has been carried out.

[0004] Among non-carbon-based negative electrode materials, silicon has a theoretical capacity reaching 4000 - 4200 mAh / g and shows a high capacity approximately 10 times or more higher than that of graphite. Therefore, it has attracted attention as a substance to replace graphite.

[0005] The negative electrode active material utilizing silicon can improve the charge-discharge capacity compared to the existing negative electrode active material utilizing carbon and increase the energy density. However, in the process of lithium ion intercalation and deintercalation, it shows a volume expansion rate exceeding 300%, so the life characteristics are not good.

[0006] On the other hand, SiO x (0.5 < x ≤ 2) has high mechanical strength due to the oxide formed during the initial charge-discharge process. As a result, the negative electrode material containing SiO x has stability against the volume expansion occurring during charge-discharge, and many attempts have been made to improve the life characteristics of secondary batteries. I

[0007] However, silicon oxide SiO x (0.5 < x ≤ 2) has a disadvantage of low initial efficiency due to an irreversible reaction in which a part of the lithium transferred to the negative electrode material during initial charging does not return to the positive electrode material during discharging.

[0008] Recently, silicon oxide (SiO x However, this technique reduces the capacity of the secondary battery, and during the manufacturing process, the active material, binder, and distilled water are dispersed in a slurry to form a slurry that is then coated onto a copper electrode plate, making industrial mass production difficult due to the reduced stability of the slurry.

[0009] Therefore, there is a need for a negative electrode material for secondary batteries that can improve the initial discharge capacity, initial efficiency, and life characteristics of secondary batteries and that can be stably mass-produced. Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide a negative electrode active material comprising a densified composite.

[0011] An object of the present invention is to provide an anode material for a secondary battery, which can improve the initial discharge capacity, initial efficiency and life characteristics of the secondary battery by using the anode active material.

[0012] Another object of the present invention is to provide a method for producing a negative electrode material for a secondary battery that can be mass-produced stably.

[0013] The objects of the present invention are not limited to those mentioned above, and other objects and advantages of the present invention not mentioned above can be understood from the following description and can be more clearly understood from the examples of the present invention. Furthermore, it is clear that the objects and advantages of the present invention can be achieved by the means and combinations thereof set forth in the claims. [Means for solving the problem]

[0014] A negative electrode material for a secondary battery, comprising an active material, a conductive material, and a binder, wherein the surface is carbon-coated according to the present invention. The active material includes a composite doped with magnesium. The composite doped with magnesium includes silicon oxide (SiO x , 0.5 < x ≤ 2) nanoparticles, silicon (Si) nanoparticles, and Magnesium oxide nanoparticles. The diameter of the Magnesium oxide nanoparticles may be 30 to 150 nm.

[0015] The weight ratio of silicon oxide nanoparticles: silicon (Si) nanoparticles: Magnesium oxide nanoparticles may be 100:80 to 120:5 to 30.

[0016] The average diameter (D50) of the composite may be 1 to 18 μm. [[ID=?]] [[ID=?]]

[0017] [[ID=?]] A method for manufacturing a negative electrode material for a secondary battery, comprising an active material, a conductive material, and a binder, wherein the surface is carbon-coated according to the present invention. The method includes: (a) mixing silicon oxide (SiO<\ x , 0.5 < x ≤ 2) nanoparticles, silicon (Si) nanoparticles, and Magnesium oxide nanoparticles to produce a mixture; (b) adding a binder to the mixture and molding it to produce a molded product; (c) heat-treating the molded product to produce a composite doped with magnesium; and (d) coating the composite doped with magnesium with carbon to produce an active material. Magnesium oxide The diameter of the nanoparticles may be 30 to 150 nm.

[0018] In the above step (b), 5 to 20 parts by weight of the binder can be added based on 100 parts by weight of the silicon oxide nanoparticles.

[0019] The step of molding in the above step (b) to produce a molded product can be carried out by compression to produce pellets or by spray drying to produce spherical powders.

[0020] It should be noted that there are some tags like Magnesium oxide , Magnesium oxide , etc. whose specific meanings are not clear from the given text. If there are specific requirements or corrections regarding these tags, please let me know.The heat treatment in step (c) may include four steps: (c1) a step of increasing the temperature from room temperature to 500°C; (c2) a step of maintaining the temperature in step 1 while performing the heat treatment; (c3) a step of increasing the temperature from the heat treatment temperature in step 2 to 1200°C; and (c4) a step of maintaining the temperature in step 3 while performing the heat treatment. [Effects of the Invention]

[0021] The negative electrode material for a secondary battery according to the present invention includes a magnesium-doped and densified composite as a negative electrode active material, and thus has the effect of improving the initial discharge capacity, initial efficiency, and life characteristics of the secondary battery.

[0022] The method for producing a negative electrode material for a secondary battery according to the present invention has the effect of enabling stable mass production of a negative electrode active material containing a composite.

[0023] The above-mentioned effects and specific effects of the present invention will be described in conjunction with the following description of the preferred embodiment of the invention. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a flow chart showing a method for producing a negative electrode material for a secondary battery according to the present invention. [Figure 2] 1 shows the results of analyzing the composite of Example 1 by XRD (Empyean equipment from Malvern Panalytical). [Figure 3] 1 shows SEM images of cross sections of composites of Example 1 to Comparative Example 3 according to the present invention and Mg distribution. DETAILED DESCRIPTION OF THE INVENTION

[0025] The above-mentioned objects, features, and advantages will be described in detail below with reference to the accompanying drawings, so that those skilled in the art can easily implement the technical concept of the present invention. In describing the present invention, if a detailed description of known technologies relating to the present invention is deemed to obscure the gist of the present invention, the detailed description will be omitted. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings are used to indicate the same or similar components.

[0026] In the following, when an arbitrary structure is arranged "on top (or bottom)" of a component or "above (or below)" a component, it means that the arbitrary structure is not only arranged in contact with the upper surface (or lower surface) of the component, but also that other structures may be interposed between the component and the arbitrary structure arranged above (or below) the component.

[0027] Furthermore, when a component is described as being "coupled," "coupled," or "connected" to another component, it should be understood that the components may be directly coupled or connected to each other, but that there may be other components "intervening" between the components, or that the components may be "coupled," "coupled," or "connected" via other components.

[0028] Hereinafter, negative electrode materials for secondary batteries and methods for manufacturing the same according to several embodiments of the present invention will be described.

[0029] The negative electrode material for a secondary battery of the present invention includes an active material whose surface is coated with carbon, a conductive material, and a binder, and the active material includes a densified composite that is doped with magnesium.

[0030] The active material contains a densified composite doped with magnesium (Mg), which has the effect of further improving the performance of the secondary battery in terms of initial discharge capacity and initial efficiency.

[0031] The magnesium-doped composite was prepared by the method described above using silicon oxide (SiOx , nano-particles with 0.5 < x ≤ 2), silicon (Si) nano-particles, and Magnesium oxide include nano-particles.

[0032] In the active material Magnesium oxide (MgO) nano-particles can be complexed with silicon oxide nano-particles and silicon (Si) nano-particles to further improve the characteristics of the secondary battery.

[0033] Magnesium oxide Since the nano-particles have a nano-size of 150 nm or less, they have excellent dispersibility, mix well with other nano-particles, and provide the effect of magnesium doping between silicon oxide nano-particles and silicon (Si) nano-particles.

[0034] The magnesium-doped composite means that a small amount of magnesium is added, magnesium is uniformly dispersed inside and outside the composite, and magnesium uniformly penetrates between the interfaces of the nano-particles.

[0035] By including a small amount of magnesium in the composite, the active material has the effect of further improving the initial discharge capacity, initial efficiency, and life characteristics of the secondary battery.

[0036] In particular, Magnesium oxide only when the nano-particles satisfy a diameter of 30 - 150 nm and are not of micrometer size can the characteristics of the secondary battery be improved. Preferably, Magnesium oxide the diameter of the nano-particles may be from 30 to 130 nm or from 30 to 80 nm.

[0037] If Magnesium oxide the diameter of the nano-particles is outside the range of 30 - 150 nm or is 1 μm or more, the dispersion characteristics of Mg are not good, agglomeration occurs, and there is a problem that it is difficult to improve the characteristics of the secondary battery.

[0038] On the other hand, if the composite Magnesium oxideIf magnesium nitrate (Mg(NO3)2) particles are used instead of (MgO) nanoparticles, problems arise in that the manufacturing stability and performance of the secondary battery are reduced.

[0039] Therefore, the complex of the present invention is Magnesium oxide Preferably, it comprises nanoparticles.

[0040] The capacity of secondary batteries is determined by silicon oxide nanoparticles and silicon (Si) nanoparticles. To reduce the solid electrolyte interface (SEI) and irreversible capacity generated during initial charging and discharging, the Mg source can be reacted with silicon or silicon oxide first to form a magnesium silicate phase, thereby reducing the irreversible capacity.

[0041] Thus, in the present invention Magnesium oxide The nanoparticles are used in a doping concept that reduces irreversible capacity, so using too much magnesium can reduce the capacity of the battery itself.

[0042] Therefore, in the complex, Magnesium oxide The content of nanoparticles is preferably less than the content of silicon oxide nanoparticles and less than the content of silicon (Si) nanoparticles.

[0043] Magnesium oxide When the content of nanoparticles is lower than the content of silicon oxide nanoparticles and silicon (Si) nanoparticles, in addition to the above-mentioned effects, the content of MgO, Si, SiO x The nanoparticles are well mixed without agglomeration, which has the effect of distributing Mg uniformly between the particle interfaces and inside the particles.

[0044] Silicon oxide nanoparticles: Silicon (Si) nanoparticles: Magnesium oxide The weight ratio of the nanoparticles may be 100:80-120:5-30. For example, the weight ratio may be 100:90-110:10-20. may be.

[0045] The silicon oxide nanoparticles in the active material act as a buffer to suppress the volume expansion of silicon.

[0046] If silicon oxide nanoparticles or silicon (Si) nanoparticles, which are not composites, were used as the active material, the silicon (Si) nanoparticles would react with lithium and undergo a volume expansion of over 300%, which could drastically reduce the lifespan of the secondary battery. To overcome this drawback, it is preferable to use silicon (Si) nanoparticles together with silicon oxide nanoparticles.

[0047] As described above, when silicon oxide nanoparticles or silicon (Si) nanoparticles are used alone, it is difficult to improve the initial discharge capacity, initial efficiency, and life characteristics of the secondary battery. Magnesium oxide It is preferred to use a composite comprising nanoparticles.

[0048] The silicon oxide nanoparticles may be crystalline and / or amorphous, and the silicon (Si) nanoparticles may be crystalline.

[0049] Silicon oxide nanoparticles and silicon (Si) nanoparticles refer to particles having a nano-sized diameter of several nm to several hundred nm, with the diameter being 1 μm or less, respectively.

[0050] The diameter of each of the silicon oxide nanoparticles and the silicon (Si) nanoparticles may be the same as or larger than the diameter of the silicon crystal particles contained in each of the nanoparticles.

[0051] The diameter of each of the silicon oxide nanoparticles and silicon (Si) nanoparticles may be 5 to 1000 nm, for example, 10 to 800 nm, 20 to 600 nm, 30 to 400 nm, or 40 to 200 nm.

[0052] The diameter of the nanoparticles can be measured using the BECKMAN COULTER life Sciences, LS 13 320 Particle Size Analyzer equipment.

[0053] Silicon oxide (SiO x , 0.5 < x ≦ 2) nanoparticles and silicon (Si) nanoparticles have silicon crystalline microparticles.

[0054] The active material shows a structure in which silicon crystalline microparticles with different diameters are dispersed while magnesium is distributed in the complex.

[0055] The crystalline microparticles in the present invention refer to a lattice regularly arranged in the space forming the nanoparticles or a solid substance arranged disorderly. The crystalline microparticles can be used as synonyms such as crystal, crystallite, crystal particle, etc.

[0056] The characteristics of the secondary battery can vary depending on the diameter (size) of the silicon crystalline microparticles.

[0057] Silicon oxide (SiO x , 0.5 < x ≦ 2) The first silicon crystalline microparticles contained in the nanoparticles are preferably different from the diameter of the second silicon crystalline microparticles contained in the silicon (Si) nanoparticles. And it is more preferable that the diameter of the first silicon crystalline microparticles is smaller than the diameter of the second silicon crystalline microparticles.

[0058] If the diameters of the first silicon crystalline microparticles and the second silicon crystalline microparticles are the same as each other or the diameter of the first silicon crystalline microparticles is larger than the diameter of the second silicon crystalline microparticles, there is a problem that it is insufficient to improve the characteristics of the secondary battery aimed at in the present invention.

[0059] Specifically, the diameter of the first silicon crystalline microparticles of the silicon oxide nanoparticles is preferably 3 to 20 nm. For example, the diameter of the first silicon crystalline microparticles may be 5 to 18 nm, or may be 7 to 16 nm.

[0060] The diameter of the second silicon crystal particles of silicon (Si) nanoparticles is preferably 20 to 50 nm, for example, the diameter of the second silicon crystal particles may be 25 to 45 nm, or may be 30 to 40 nm.

[0061] By ensuring that the diameter of the first silicon crystal microparticles is 3 to 20 nm and the diameter of the second silicon crystal microparticles is 20 to 50 nm, the initial discharge capacity and initial efficiency of the secondary battery can be improved, and stable life characteristics can be obtained.

[0062] The diameter of the silicon crystal particles can be measured using X-ray diffraction (XRD, equipped with Empyean from Malvern Panalytical Co.). For example, the FWHM (2 Θ ) value is measured, and the crystal size can be calculated using the value by the XRD half-width method.

[0063] The weight ratio of the first silicon crystal microparticles to the second silicon crystal microparticles in the composite may be 100:80 to 120. For example, the weight ratio may be 100:90 to 110, or 100:95 to 105.

[0064] By ensuring that the weight ratio of the first silicon crystal microparticles to the second silicon crystal microparticles satisfies 100:80-120, when the composite is applied to a secondary battery as a negative electrode material, the initial discharge capacity, initial efficiency, and life characteristics can be further improved compared to conventional secondary batteries.

[0065] The molar ratio of oxygen (O):silicon (Si) in the composite may be 0.5:1.0 to 1.0:1.0. When the molar ratio of oxygen to silicon satisfies 0.5 to 1.0, the life characteristics of the secondary battery can be further improved.

[0066] In this way, the active material may be a composite in which three types of nanoparticles are uniformly distributed, and first silicon crystal microparticles and second silicon crystal microparticles having different diameters are dispersed inside and on the surface.

[0067] The composite is composed of silicon oxide nanoparticles, silicon (Si) nanoparticles, and Magnesium oxide The nanoparticles may not be simply mixed, but may be mixed with each other and be highly densely composited.

[0068] The composite can be densified by binder treatment and stepwise heat treatment in the manufacturing method described below. Forming a high-density composite has the effect of further improving the initial efficiency and life characteristics of the secondary battery.

[0069] The high density can be determined by the specific surface area (BET), and provides the effect of suppressing the volume expansion of silicon.

[0070] The specific surface area of ​​the composite is 1 to 17 m 2 For example, the specific surface area may be 3 to 10 m 2 / g, and 3.3 to 4m 2 / g.

[0071] Specific surface area is 1 to 17 m 2 If the content is outside of this range, many voids are formed in the composite, which may be insufficient to exhibit secondary battery properties.

[0072] The specific surface area of ​​the composite can be measured by analyzing the specific surface area by nitrogen adsorption using the Brunauer-Emmett-Teller (BET) equation (analysis equipment: BEL Japan Inc, BELSORP-max).

[0073] These densified composites preferably have a micrometer size.

[0074] The micrometer size of the composite can provide the advantage that it is advantageous to form a densified composite.

[0075] The average diameter (D50) of the complex is preferably 1 to 18 μm.

[0076] For example, the average diameter (D50) of the complex may be 3 to 15 μm, for example, 5 to 11 μm.

[0077] The average diameter (D50) of the complex can be defined as the diameter at 50% of the diameter distribution. The average diameter (D50) can be measured using a PSA analysis device - BECKMAN COULTER Life Sciences, LS 13 320 Particle Size Analyzer. For example, after dispersing the complex in a solution, the average diameter of the complex at 50% of the diameter distribution can be calculated.

[0078] The active material constituting the negative electrode material preferably contains a composite whose surface is coated with carbon in order to prevent oxidation of silicon (Si) nanoparticles.

[0079] The carbon coating layer formed on the surface of the composite utilizes high softening point pitch (HSPP) to form on the surface of the silicon composite, which is close to being a non-conductor, and can provide conductivity. The carbon coating layer also acts as a protective film for the composite, reducing the interfacial resistance between the anode material and the electrolyte, improving interfacial stability over time. Therefore, when a composite with a carbon coating layer is used as an anode material for a secondary battery, it can improve charge / discharge efficiency and lifespan characteristics.

[0080] The second carbon material contained in the carbon coating layer may be located on the entire surface of the composite or on a portion of the surface, and is preferably formed with a uniform thickness over the entire surface of the composite in consideration of the effect of improving the physical properties of the negative electrode material.

[0081] For 100% by weight of the composite whose surface is carbon-coated, the composite may contain 80-95% by weight of the composite and 5-20% by weight of the carbon coating layer. For example, the composite may contain 90-95% by weight of the composite and 5-10% by weight of the carbon coating layer. When the carbon coating layer (second carbon material) content is 5-20% by weight, the stability of the composite can be improved and the interfacial resistance between the negative electrode material and the electrolyte can be reduced. If the carbon coating layer content exceeds 20% by weight, there is a problem of a decrease in the initial capacity of the secondary battery.

[0082] The thickness of the carbon coating layer may be, but is not limited to, 0.1 to 10 nm.

[0083] The second carbon material may include one or more of natural graphite, artificial graphite, mesocarbon microbeads, and high softening point pitch.

[0084] Pitch is made by heat-treating the residue from petroleum distillation, and has a high carbonization yield and low impurity content. This pitch improves the charge / discharge efficiency of secondary batteries, thereby extending their lifespan.

[0085] High softening point pitch refers to pitch with a softening point of 200 to 300°C.

[0086] The active material constituting the negative electrode material can be used as a composite alone, but can also be used together with the first carbon material.

[0087] When the active material includes the composite and the first carbon material, the characteristics of the secondary battery can be further improved, the conductivity can be increased, and the life characteristics can be further improved.

[0088] In particular, it can improve the electrical conductivity between active materials, thereby improving the electrochemical properties of the electrolyte, and it can reduce the volume expansion of silicon (Si) nanoparticles, thereby extending the life of the secondary battery.

[0089] The first carbon material may contain natural graphite, artificial graphite, graphitized carbon fiber, amorphous carbon, or the like, which are generally used in negative electrode active materials.

[0090] The weight ratio of the composite to the first carbon material in the active material may be 1:1 to 1:7. For example, the weight ratio of the composite to the first carbon material may be 1:2 to 1:6, or 1:3 to 1:5.

[0091] The negative electrode material for a secondary battery may contain a conductive material and a binder in addition to the active material.

[0092] The conductive material may be contained in order to impart electrical conductivity to the negative electrode material, and any material that has electrical conductivity without causing chemical changes can be used without any restrictions.

[0093] For example, the conductive material may include one or more of a third carbon material, a metal powder, a metal fiber, a conductive whisker, a metal oxide, and a conductive polymer.

[0094] The binder plays a role in improving the binding between active materials and the adhesive strength between the active materials and the current collector, and may contain a water-based binder among binders normally used in negative electrode materials.

[0095] For example, the aqueous binder may contain one or more of polyvinyl alcohol, starch, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, acrylic rubber, styrene-butadiene rubber (SBR), regenerated cellulose, hydroxypropyl cellulose, carboxymethyl cellulose (CMC), and fluorine-based rubber.

[0096] The weight ratio of active material:conductive material:binder in the negative electrode material for secondary batteries may be 100:0.1-5:1-20. For example, the weight ratio of active material:conductive material:binder may be 100:0.5-3:2-7.

[0097] Thus, among the negative electrode materials for secondary batteries of the present invention, the active material contains a magnesium-doped and densified microcomposite, thereby suppressing volume expansion and enabling the production of a negative electrode material with high capacity.

[0098] As a result, the active material of the present invention is very effective for a negative electrode material that can improve the characteristics of the energy storage material, and can be applied to a secondary battery using a non-aqueous electrolyte.

[0099] Furthermore, the active material of the present invention can be applied as a negative electrode material for secondary batteries to IT materials, electric vehicles, and the like.

[0100] The manufacturing method of the negative electrode material for secondary batteries of the present invention will be described in detail.

[0101] FIG. 1 is a flowchart showing the manufacturing method of the negative electrode material for secondary batteries according to the present invention.

[0102] Referring to FIG. 1, the manufacturing method of the active material among the negative electrode materials for secondary batteries according to the present invention includes a step (S x 110) of mixing silicon oxide (SiO Magnesium oxide x, 0.5 < x ≤ 2) nanoparticles, silicon (Si) nanoparticles and

[0103] nanoparticles to produce a mixture, a step (S120) of adding a binder and molding to produce a molded product, a step (S130) of heat-treating to produce a magnesium-doped composite, and a step (S140) of coating with carbon to produce an active material.

[0104] The method for manufacturing the active material among the negative electrode materials for secondary batteries of the present invention is as follows.

[0105] First, silicon oxide (SiO x, nanoparticles where 0.5 < x ≤ 2, silicon (Si) nanoparticles, and Magnesium oxide Mix the nanoparticles to produce a mixture.

[0106] Silicon oxide nanoparticles, silicon (Si) nanoparticles, and Magnesium oxide After dispersing the nanoparticles in an alcoholic solvent such as ethanol and / or distilled water, they can be pulverized by ball milling to provide a mixture.

[0107] As the magnesium (Mg) precursor, Magnesium oxide When using one or more of magnesium hydroxide (Mg(OH)₂) particles, magnesium nitrate (Mg(NO₃)₂) particles, magnesium (Mg) nanoparticles, and magnesium gas instead of (MgO) nanoparticles, the dispersibility in a solvent or distilled water is low, and it is difficult to produce a dispersion solution together with silicon oxide nanoparticles and silicon (Si) nanoparticles. Also, problems occur in the stability of production. As a result, the reaction in the subsequent stage is not sufficiently carried out, and a composite with deteriorated physical properties is obtained.

[0108] Therefore, as the magnesium precursor, Magnesium oxide It is preferably included nanoparticles having a diameter of 30 to 150 nm, Magnesium oxide More preferably, it is included nanoparticles.

[0109] Silicon oxide nanoparticles: silicon (Si) nanoparticles: Magnesium oxide The weight ratio of the nanoparticles may be 100:80 to 120:5 to 30.

[0110] The steps of dispersion and pulverization can be carried out for 1 to 10 hours, for example, 1 to 5 hours. When the dispersion and pulverization time is less than 1 hour, the pulverization effect of the nanoparticles may be insufficient. Conversely, when it exceeds 10 hours, the pulverization time is too long, and the process may be inefficient.

[0111] As described above, the diameter of the first silicon crystal particles of silicon oxide nanoparticles is preferably different from the diameter of the second silicon crystal particles of silicon (Si) nanoparticles.

[0112] The first silicon crystal particles of silicon oxide nanoparticles may have a diameter of 3 to 20 nm, and the second silicon crystal particles of silicon (Si) nanoparticles may have a diameter of 20 to 50 nm.

[0113] The matters relating to silicon oxide nanoparticles, silicon (Si) nanoparticles and silicon crystal fine particles are the same as those described above.

[0114] Next, a binder is added to the mixture and the mixture is molded to produce a molded product.

[0115] Adding a binder to the mixture allows for the formation of silicon oxide nanoparticles, silicon (Si) nanoparticles, and Magnesium oxide The adhesive strength of the nanoparticles is improved, allowing the diameter of the composite to be formed in the micron order, and a dense structure can be formed.

[0116] During the stepwise heat treatment process described below, silicon oxide nanoparticles, silicon (Si) nanoparticles, and Magnesium oxide As the binder on the surface of the nanoparticles and the binder between the nanoparticle interfaces burn out, voids are formed where the binder was, providing a binding force between the nanoparticles and allowing the composite to become denser.

[0117] The binder affects the density and pore characteristics of the composite, and the density and pore characteristics affect the characteristics of the secondary battery.

[0118] Therefore, in order to satisfy the initial efficiency and life characteristics of the secondary battery, it is important to add a binder to the mixture, dry it, and then heat-treat the molded product.

[0119] The binder may be an aqueous binder and may contain one or more of polyvinyl alcohol, starch, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, acrylic rubber, styrene-butadiene rubber (SBR), regenerated cellulose, hydroxypropyl cellulose, carboxymethyl cellulose (CMC), and fluorine-based rubber.

[0120] Preferably, the binder may include one or more of styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC).

[0121] To achieve both high density and micronization of the composite, 5 to 20 parts by weight of binder can be added to 100 parts by weight of silicon oxide nanoparticles, for example, 5 to 18 parts by weight of binder can be added.

[0122] To make the mixture with the binder added into a micrometer-sized powder (molded product), one of two methods can be selected and used.

[0123] In the first method, the mixture to which the binder has been added is pulverized and dispersed by a ball mill, and then dried, and the dried powder is then compressed to produce a pellet-shaped powder.

[0124] The grinding and dispersion can be carried out for 1 to 10 hours, for example, 1 to 5 hours.

[0125] The diameter of the pelleted powder is much larger than the diameter of the powder dried before compaction, and said pelleted powder can take advantage of the benefits of being micronized.

[0126] Compression can be accomplished by, but is not limited to, hot pressing, casting, extrusion, and the like.

[0127] The second method can be spray drying to produce a spherical powder.

[0128] Spray drying is a technique for rapidly drying a liquid material with hot air to produce a powdered material, and can be carried out using a spray dryer equipped with a sprayer, heater, and dryer that atomizes the liquid material.

[0129] Spray drying allows for the adjustment of particle size, shape, etc. depending on various conditions such as experimental conditions and liquid state, and is suitable for mass production.

[0130] The compacted powder is then stepwise heat treated to produce the magnesium doped composite.

[0131] The stepwise heat treatment can be performed in four stages: stage 1, in which the temperature is increased from room temperature (25±1°C) to 500°C at an average heating rate of 1 to 5°C / min; stage 2, in which the heat treatment is maintained at stage 1 temperature for 30 minutes to 3 hours; stage 3, in which the temperature is increased from stage 2 heat treatment temperature to 1200°C at an average heating rate of 10 to 20°C / min; and finally, stage 3, in which the heat treatment is maintained at stage 3 temperature for 30 minutes to 3 hours.

[0132] Preferably, the molded product can be sintered in four stages: a first stage in which the temperature is increased from room temperature to 450 to 550°C; a second stage in which the temperature is maintained at 450 to 550°C, which is the same temperature range as in the first stage; a third stage in which the temperature is increased from the heat treatment temperature in the second stage to 1150 to 1250°C; and a fourth stage in which the temperature is maintained at 1150 to 1250°C, which is the same temperature range as in the third stage.

[0133] During the temperature rise to near 500°C and near 1200°C, the molded product is continuously heat-treated at these temperatures.

[0134] In particular, the present invention relates to silicon oxide nanoparticles, silicon (Si) nanoparticles, Magnesium oxideAfter heat-treating the nanoparticle-containing molded product at around 500°C, a final heat treatment at an even higher temperature of around 1200°C can increase the density of the composite, which suppresses the volumetric expansion of silicon and improves the performance of secondary batteries. In particular, the disproportionation reaction in the final heat treatment stage decomposes silicon oxide nanoparticles into SiO2 and Si, allowing silicon crystal particles to be uniformly dispersed.

[0135] In this respect, the stepwise heat treatment of the present invention is different from the existing heat treatments which involve one or more heat treatments in one temperature range or two heat treatments in different temperature ranges.

[0136] When using pellet-shaped powder, after stepwise heat treatment, it is subjected to primary grinding in a coarse grinder and then pulverized in a ball mill to produce a high-density composite with an average diameter (D50) of 3 to 15 μm.

[0137] The pulverization can be carried out for 1 to 10 hours, for example, 1 to 5 hours. The matters regarding the average diameter (D50) of the complexes are the same as those described above.

[0138] When spray drying is used, the grinding and milling steps can be omitted.

[0139] The magnesium-doped composite is then coated with carbon to produce the active material.

[0140] The carbon coating may be applied to impart conductivity, increase the stability of the composite, and reduce reactivity to moisture and oxygen.

[0141] By wet coating the second carbon material and carbonizing it at 800 to 1200°C in an inert atmosphere, a carbon coating layer that acts as a protective film can be formed on the surface of the composite.

[0142] Specifically, the wet coating process can be carried out in three steps: the first step is dissolving the second carbon material in an organic solvent such as THF; the second step is dissolving the silicon oxide composite in an organic solvent such as THF; and the second step is mixing the solutions from the first and second steps, removing only the solvent, drying, and then carbonizing.

[0143] The carbon coating can be performed at 900 to 1100° C. The inert atmosphere may contain one or more of argon (Ar) gas, nitrogen (N2) gas, helium (He) gas, and xenon (Xe) gas.

[0144] The second carbon material can be added in an amount of 5 to 20% by weight, for example 5 to 10% by weight, based on 100% by weight of the composite having a carbon-coated surface.

[0145] The carbon coating layer may include one or more second carbon materials selected from the group consisting of natural graphite, artificial graphite, mesocarbon microbeads, and high softening point pitch.

[0146] After preparing the composite whose surface is coated with carbon, the composite and the first carbon material are further mixed in a weight ratio of 1:1 to 1:7 to prepare an active material.

[0147] The matters relating to the active material containing silicon oxide and the first carbon material are the same as those described above.

[0148] Next, the active material, conductive material, and binder are mixed in a weight ratio of 100:0.1-5:1-20 to prepare a slurry, and then the slurry is coated on a current collector to prepare a negative electrode material.

[0149] The weight ratios of the active material, conductive material, and binder are the same as those described above.

[0150] The current collector can be used without limitation as long as it is a material that does not cause chemical changes in the secondary battery and has conductivity. For the current collector, for example, copper, aluminum, nickel, etc. can be used.

[0151] Thus, when considering specific examples of the negative electrode material for the secondary battery, it is as follows.

[0152] 1. Manufacture of the composite Example 1 Silicon oxide nanoparticles SiO with a diameter of 50 to 100 nm x (0.5 < x ≤ 2) (diameter of Si crystalline microparticles: 3 to 20 nm), silicon (Si) nanoparticles with a diameter of 128 nm (diameter of Si crystalline microparticles: 20 to 50 nm), with a diameter of 33 to 66 nm Magnesium oxide The nanoparticles were mixed at a weight ratio of 100:100:15 to provide a mixture. The weight ratio of Si crystalline microparticles of the silicon oxide nanoparticles to Si crystalline microparticles of the silicon nanoparticles is 100:100.

[0153] After dispersing 5 parts by weight of a binder (SBR, CMC) in 100 parts by weight of silicon oxide nanoparticles in distilled water, the above mixture was added and dispersed at 1200 rpm using a homogenizer.

[0154] Next, spray drying was performed using a spray dryer equipment (Ein System Co., Ltd.) to obtain dried spherical powder with D10 of 2.07 μm, D50 of 6.23 μm, and D90 of 11.13 μm. The dried spherical powder was heat-treated in four steps. In the first step, the temperature was raised to 500 °C at 1 °C / min. In the second step, it was maintained at 500 °C for 1 hour. In the third step, the temperature was raised to 1200 °C at 10 °C / min, and in the last step, sintering treatment was performed while maintaining at 1200 °C for 5 hours.

[0155] To carbon coat the Mg-doped composite, a high softening point pitch (OCI developed product) was wet-coated so that the carbon content was at the 10 wt% level with respect to 100 wt% of the final particles. The wet coating involved dissolving the HSPP in THF, dissolving the composite in THF, mixing the two solutions, and then using an evaporator to evaporate and dry at 35 - 40 °C under hot water bath conditions.

[0156] Next, through a carbonization process at 1000 °C and in a nitrogen atmosphere, a composite with a carbon-coated surface as the final particles was obtained.

[0157] Comparative Example 1 As starting materials, silicon oxide nanoparticles SiO with a diameter of 50 - 100 nm x (0.5 < x ≤ 2) (the diameter of Si crystalline microparticles is 3 - 20 nm) were used, and a composite with a carbon-coated surface was obtained in the same manner as in Example 1, except that a CMC binder was used.

[0158] Comparative Example 2 Silicon oxide nanoparticles SiO with a diameter of 50 - 100 nm x (0.5 < x ≤ 2) (the diameter of Si crystalline microparticles is 3 - 20 nm) were provided.

[0159] After dispersing 5 parts by weight of a binder (CMC) with respect to 100 parts by weight of silicon oxide nanoparticles in distilled water, the silicon oxide nanoparticles were added and dispersed at 1200 rpm using a homogenizer.

[0160] Next, spray drying was carried out using a spray dryer equipment (Ain System Co., Ltd.) to obtain a dried spherical powder with D10 of 2.07 μm, D50 of 6.23 μm, and D90 of 11.13 μm. The dried spherical powder was heat-treated in four steps. In the first step, the temperature was raised to 500 °C at 1 °C / min. In the second step, it was maintained at 500 °C for 1 hour. In the third step, the temperature was raised to 1200 °C at 10 °C / min, and in the last step, sintering treatment was carried out while maintaining at 1200 °C for 5 hours.

[0161] Next, magnesium hydroxide Mg(OH)2 (Sigma-Aldrich) was dispersed in distilled water to prepare a solution, and then doped on the outside of the sintered powder by a wet method. After that, it was dried and heat-treated at 1200 °C to produce a magnesium-doped magnesium silicate (Mg2SiO4) composite.

[0162] To carbon coat the produced composite, high softening point pitch (OCI developed product) was wet-coated to a carbon content level of 10% by weight based on 100% by weight of the final particles. The wet coating was carried out by dissolving HSPP in THF, dissolving the composite in THF, mixing the two solutions, and then using an evaporator to evaporate and dry at 35 - 40 °C under a hot water bath condition.

[0163] Next, through a carbonization process at 1000 °C in a nitrogen atmosphere, a composite with a carbon-coated surface was obtained as the final particles.

[0164] Comparative Example 3 Silicon oxide nanoparticles SiO with a diameter of 50 - 100 nm x (0.5 < x ≦ 2) (diameter of Si crystalline microparticles 3 - 20 nm), silicon (Si) nanoparticles with a diameter of 128 nm (diameter of Si crystalline microparticles 20 - 50 nm), and magnesium hydroxide Mg(OH)2 (Sigma-Aldrich) were provided in a weight ratio of 100:100:27. The weight ratio of Si crystalline microparticles of the silicon oxide nanoparticles to Si crystalline microparticles of the silicon nanoparticles is 100:100.

[0165] After dispersing 5 parts by weight of a binder (SBR, CMC) in distilled water with respect to 100 parts by weight of silicon oxide nanoparticles, magnesium hydroxide Mg(OH)2 was added and dispersed, and then silicon oxide nanoparticles and silicon (Si) nanoparticles were added and dispersed at 1200 rpm using a homogenizer.

[0166] The mixture was then spray-dried using a spray dryer (Ein System Co., Ltd.) to obtain dried spherical powder with sizes of D10 2.07 μm, D50 6.23 μm, and D90 11.13 μm. The dried spherical powder was heat-treated in two stages. In the first stage, the temperature was raised to 1200°C at a rate of 10°C / min, and in the second stage, the powder was sintered at 1200°C for 1 hour.

[0167] To carbon-coat the Mg-doped composite, high-softening-point pitch (developed by OCI) was wet-coated so that the carbon content was 10% by weight relative to the final particle weight (100% by weight). For the wet coating, HSPP was dissolved in THF, and the composite was dissolved in THF. The two solutions were then mixed and evaporated to dryness in a water bath at 35-40°C using an evaporator.

[0168] Next, the particles were subjected to a carbonization process at 1000°C in a nitrogen atmosphere to obtain composites with carbon-coated surfaces as final particles.

[0169] 2. Manufacturing of negative electrode materials for secondary batteries Each of the carbon-coated composites of Example 1 and Comparative Examples 1 to 3 was dry-mixed with artificial graphite in a weight ratio of 1:4.9 to prepare a negative electrode active material.

[0170] Next, the negative electrode active material, conductive material (artificial graphite), and binder (CMC:SBR=3:7) were mixed in a weight ratio of 100:1.1:5.3 to prepare a slurry.

[0171] The prepared slurry was coated onto a copper plate having a thickness of 10 μm.

[0172] 3. Evaluation method of physical properties and results Table 1 below shows the pore size, specific surface area, densification status, and diameter of the carbon-coated composite. Table 2 below shows the electrochemical properties of the anode material.

[0173] 1) Specific surface area: The surface area of ​​the composite was measured using BELSORP-max (BEL Japan Inc.).

[0174] 2) Presence or absence of densification: When the cross section of the composite was visually observed using an SEM, if pores (pores) were present in 10% or less, it was marked as "O", and if they were present in more than 10%, it was marked as "X".

[0175] 3) Diameter: The average diameter (D50) of the complexes was measured using a Beckman Coulter Life Sciences, LS 13 320 Particle Size Analyzer.

[0176] 4) Initial discharge capacity and initial efficiency: The initial discharge capacity and initial efficiency were measured using a half-cell device, TOSCAT-3100.

[0177] 5) Life (@50 cycles): Life characteristics were measured using a half-cell device, TOSCAT-3100.

[0178] [Table 1]

[0179] [Table 2]

[0180] Referring to Tables 1 and 2, Example 1 contains silicon oxide nanoparticles, silicon nanoparticles, and Magnesium oxide It can be seen that the nanoparticles were heat-treated in four stages together with a binder to produce a micro-sized composite that was uniformly doped with Mg.

[0181] Furthermore, Example 1 was excellent in terms of specific surface area, presence or absence of densification, and average diameter of the composite, and also showed excellent results in terms of initial discharge capacity, initial efficiency, and life characteristics.

[0182] Figure 2 shows the results of XRD (Empyean equipment from Malvern Panalytical) of the composite of Example 1. Referring to Figure 2, a peak of Mg2SiO4 is observed, confirming the presence of MgO in the composite.

[0183] 3 shows SEM images and Mg distribution of the cross section of the composites of Example 1 to Comparative Example 3 according to the present invention. The SEM images were checked to confirm whether the specific surface area (BET) values ​​in Table 1 matched visually. The Mg distribution was the EDX result of the SEM analysis.

[0184] Referring to Figure 3, Magnesium oxide It can be seen that Example 1 using nanoparticles is the most uniformly doped with Mg and has the highest density.

[0185] On the other hand, Comparative Example 1 contained only silicon oxide nanoparticles, and the composite was highly densified. The life characteristics were similar to those of Example 1, but the initial discharge capacity and initial efficiency were lower than those of Example 1.

[0186] Comparative Example 2 does not contain silicon (Si) nanoparticles, but instead contains micrometer-sized magnesium hydroxide particles. When magnesium hydroxide particles are used as the Mg precursor, their low dispersibility in water makes it difficult to prepare a dispersion solution with silicon oxide. For this reason, the magnesium hydroxide precursor was dispersed in ethanol, and Mg was doped into the exterior of the composite using a wet method.

[0187] In Comparative Example 2, micrometer-sized magnesium hydroxide particles were used, so densification was not performed, and the magnesium hydroxide was not well dispersed, resulting in the Mg clumping, which resulted in relatively low electrochemical properties.

[0188] In Comparative Example 3, micrometer-sized magnesium hydroxide particles were used and heat treatment was performed in two stages, resulting in a significantly high specific surface area and a lack of particle micronization and densification. Furthermore, the use of micrometer-sized magnesium hydroxide particles resulted in uneven doping of Mg.

[0189] From these results, Example 1 of the present invention is Magnesium oxide It can be seen that the initial discharge capacity, initial efficiency, and life characteristics were further improved compared to Comparative Examples 1 to 3 by satisfying the conditions for the diameter of the nanoparticles, binder treatment, and stepwise heat treatment.

[0190] Although the present invention has been described above with reference to illustrative drawings, the present invention is not limited to the embodiments and drawings disclosed in this specification, and it is obvious that various modifications can be made by those skilled in the art within the scope of the technical concept of the present invention. Furthermore, even if the effects of the configuration of the present invention are not explicitly described and explained while the embodiments of the present invention are described above, it is natural that the effects that can be predicted by the configuration should also be recognized.

Claims

1. A negative electrode material for a secondary battery, comprising an active material whose surface is coated with carbon, a conductive material, and a binder, the active material comprises a magnesium-doped composite; The magnesium-doped composite is Silicon oxide (SiO ｘ , 0.5<x≦2) nanoparticles, silicon (Si) nanoparticles and magnesium oxide nanoparticles; The diameter of the magnesium oxide nanoparticles is 30 to 150 nm. Negative electrode material for secondary batteries.

2. the weight ratio of silicon oxide nanoparticles:silicon (Si) nanoparticles:magnesium oxide nanoparticles is 100:80-120:5-30; The negative electrode material for a secondary battery according to claim 1 .

3. The diameter of the first silicon crystal particles of the silicon oxide nanoparticles is different from the diameter of the second silicon crystal particles of the silicon (Si) nanoparticles. The negative electrode material for a secondary battery according to claim 1 .

4. The average diameter (D50) of the complex is 1 to 18 μm. The negative electrode material for a secondary battery according to claim 1 .

5. The specific surface area (BET) of the composite is 1 to 17 m ２ / g, The negative electrode material for a secondary battery according to claim 1 .

6. The active material further includes a first carbon material. The negative electrode material for a secondary battery according to claim 1 .

7. The weight ratio of the active material:conductive material:binder in the negative electrode material for secondary batteries is 100:0.1 to 5:1 to 20. The negative electrode material for a secondary battery according to claim 1 .

8. A method for producing a negative electrode material for a secondary battery, the negative electrode material comprising an active material whose surface is coated with carbon, a conductive material, and a binder, the method comprising: (a) Silicon oxide (SiO ｘ , 0.5<x≦2) nanoparticles, silicon (Si) nanoparticles and magnesium oxide nanoparticles to prepare a mixture; (b) adding a binder to the mixture and molding it to produce a molded product; (c) heat treating the compact to produce a magnesium-doped composite; and (d) coating the magnesium-doped composite with carbon to produce an active material; The diameter of the magnesium oxide nanoparticles is 30-150 nm. A method for manufacturing negative electrode materials for secondary batteries.

9. the weight ratio of silicon oxide nanoparticles:silicon (Si) nanoparticles:magnesium oxide nanoparticles is 100:80-120:5-30; The method for producing the negative electrode material for secondary batteries according to claim 8.

10. The diameter of the first silicon crystal particles of the silicon oxide nanoparticles is different from the diameter of the second silicon crystal particles of the silicon (Si) nanoparticles. The method for producing the negative electrode material for secondary batteries according to claim 8.

11. In the step (b), 5 to 20 parts by weight of a binder is added to 100 parts by weight of the silicon oxide nanoparticles. The method for producing the negative electrode material for secondary batteries according to claim 8.

12. The step of producing a molded product by molding in the step (b) includes: Compressed to produce pellets or spray dried to produce spherical powders; The method for producing the negative electrode material for secondary batteries according to claim 8.

13. The heat treatment in the above step (c) is (c1) One step of increasing the temperature from room temperature to 500°C; (c2) A second step of heat treating the mixture while maintaining the temperature at the first step; (c3) A third stage in which the temperature is increased from the heat treatment temperature of the above two stages to 1200°C; (c4) A fourth step of heat treating the mixture by maintaining the temperature at the three steps; The method for producing the negative electrode material for secondary batteries according to claim 8.

14. The average diameter (D50) of the complex is 1 to 18 μm. The method for producing the negative electrode material for secondary batteries according to claim 8.

15. After step (d), (e) further mixing the composite and the first carbon material in a weight ratio of 1:1 to 1:7 to prepare an active material; and (f) further comprising the step of preparing a slurry by mixing the active material, the conductive material, and the binder in a weight ratio of 100:0.1-5:1-20; The method for producing the negative electrode material for secondary batteries according to claim 8.

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